At the end of the Daily Mail's report of a YouGov poll today, a spokesman for the pollster is quoted as saying: "When we take all factors into account, including the incumbency "bonus" likely to be enjoyed by Conservative MPs newly elected in 2010, Labour and the Conservatives both need around a 7 per cent lead in order to secure an overall majority in 2015". The comment is a reminder that our series this week on what David Cameron's negotiation red lines is timely.

Respondents to our poll have had their say on where those lines should be drawn. Here is mine. It's important to remember what would happen were the Liberal Democrats – or perhaps another minority party – to step over them and refuse to move. Cameron would have either to back down, or break off the talks. The consequence could be a Conservative minority government…or a Lab/Lib coalition…or even a Labour minority government. There's no way of knowing.

In the event of Cameron leading the largest party after the 2015 election, it may be that the best course will be for the Conservatives to go it alone. But in my view, that is not a decision that can be fixed on now. In such circumstances, a second Coalition could be the best option available to the country and the Party, if the right terms can be agreed. And that means red lines – not, I believe, lots of little dabs on the pavement, but a few clear markings. My top three would be:

The elimination of the structural deficit by 2017 or earlier. It may be that Vince Cable, and the Liberal Democrats as a whole, change their view on the desirability of ending the deficit swiftly: the Business Secretary's New Statesman article earlier this year hinted at such a view. This would destroy the foundation on which the present Coalition was built, and render a second one unworkable from the start – since it would have no agreed economic aim.

The holding of an EU In-Out referendum in 2017. The EU's gradual but relentless move towards "ever-closer union" has gradually made a second referendum impossible to avoid – and right. Furthermore, Conservative MPs would not allow Cameron to back down on the referendum commitment, given the strength of feeling in the Party. I am less exercised by the details of a renegotiation, since the referendum will give the British people the option of voting to leave.

Measures to rebalance the UK's political system. This is essential in both constitutional and political terms. The present settlement is unjust both to England and the Conservatives. The Liberal Democrats have succeeded in steering reform deep into the long grass during this Parliament. Were they to do so in a second one, the present Tory electoral disadvantage would stay set in stone – and the 2020 election would be looming into view, with little prospect of the majority that has eluded us for over 20 years.